PROJECT SUMMARY Health risk behaviors, such as substance use, are most prevalent during young adulthood and can lead to addiction. Thus, it is crucial to identify factors that contribute to growth in these health risk behaviors during young adulthood. A key feature of young adult health risk behaviors is delay or deficit in cognitive self-control of impulses. This is because prefrontal regions of the brain?regions critical to impulse control?are still maturing across young adulthood, a critical period of developmental transition with increasing independence in social contexts imbued with greater risk-taking opportunities. Current neurobiological models focus on developmental imbalance between the brain?s control and reward systems to explain the normative heightened risk taking seen in adolescence. Yet, little is known about individual differences in brain development underlying risky decision-making that leads to escalation of health risk behaviors from adolescence to young adulthood. This application proposes to continue a longitudinal study of 167 adolescents (13/14 to 16/17 years) throughout young adulthood (18/19 to 21/22 years) with intensive, repeated, multiple-level data (including neuroimaging, behavioral performance, and self- and parent report). The sample involves adolescents from understudied Appalachian rural communities that have high rates of substance abuse/addiction, and more recently an opioid/heroin overdose crisis. The objective is to clarify dynamic interactions between developmental trajectories of neural processes?risk/reward processing (valuation system) and cognitive control (control system)?that produce differential vulnerability to health risk behaviors in adolescence and young adulthood. The central hypotheses are: (1) the interplay between valuation and control systems contributing to health risk behaviors will be shown by statistical interactions between valuation and control neural activations as well as patterns of between-system connectivity; and (2) socioecological context effects on neural processes will clarify conditions under which adolescent brain development may become impoverished, and ultimately lead to suboptimal health behavior in young adulthood. The specific aims are to examine long-term prospective effects of brain development in adolescence on health risk behaviors in young adulthood as well as reciprocal effects of health risk behaviors on brain development (Aim 1) and to examine effects of socioeconomic adversity (e.g., scarcity, low income-to-need ratio) in adolescence on health risk behaviors in young adulthood, partially mediated through parenting contexts (e.g., parent self-regulation and maladaptive parenting), with socioeconomic contextual factors that are unique to young adulthood (e.g., college attendance) predicting young adult health risk behaviors (Aim 2). These findings will yield critical insights into the neural mechanisms underlying susceptibility to health risk behaviors in adolescence and young adulthood and contextual influences on these mechanisms, with the potential to inform optimally-timed, targeted prevention efforts to ameliorate developmental pathways of youth who are at risk for drug addiction.